This invention relates to an ultrasonic sealing apparatus for fuse-bonding sheet-like members formed of thermoplastic resin, and more particularly to an improvement of horn and anvil means in such apparatus capable of fuse-bonding opposing sheets with frictional heat generated by the ultrasonic vibration.
Various types of ultrasonic sealing apparatus have been known in which a pair of sheet-like members are fuse-bonded together by means of ultrasonic vibration. Firstly, a vertical vibration type sealing apparatus has been proposed in which ultrasonic vibration is applied to the fuse-bonding surface in a direction perpendicular thereto. According to this apparatus, lateral displacement of the sheet-like members relative to the horn and anvil means can be eliminated, since the fuse-bonding surfaces of the sheets are subject to the vibration in a direction perpendicular to the surfaces. Therefore, it is unnecessary to provide an embossing pattern on the sealing surfaces of the horn and anvil means for eliminating the lateral displacement. However, it is impossible to laterally remove or displace foreign materials adhered to the fuse-bonding surface of the sheets during vibration, due to the vibrating direction. Therefore, the vertical vibration type would not be available for fuse-bonding the bottom portion of a tubular container for containing cosmetics.
Secondly, lateral vibration type sealing apparatus have been proposed in which ultrasonic vibration is applied in a direction parallel to the fuse-bonding surfaces of the sheets. According to this type, foreign particles adhered to the fuse-bonding surfaces of the sheets can be removed in a lateral direction of the sheets because of the lateral vibration. However, lateral displacement of the sheets may occur with respect to the horn and anvil means due to the lateral vibration. This lateral displacement provides disadvantages in that ultrasonic vibration may not be efficiently transmitted to the fuse-bonded surfaces of the sheets, while the heat generation occurs at the horn means. Further, sufficient fuse-bonding may not be obtainable due to shortage of frictional heat during vibration, and furthermore, unpleasant high sound noise is generated due to the lateral displacement. Moreover, at the surfaces of the sheets in contact with the horn and anvil means partial hangnail or shaved-cut tips may be generated.
In order to obviate the above-described problems attendant to the lateral-vibration type sealing apparatus, an embossed pattern as shown in FIGS. 12A and 12B is formed on the surfaces of the horn and anvil means at portions in direct contact with the sheets. However, the embossed pattern shown in FIGS. 12A and 12B still did not provide a satisfactory result.
Thirdly, oblique vibration type sealing apparatus have been proposed in which ultrasonic vibration is applied to the fuse-bonding surfaces of the sheets in an oblique direction with respect to the surfaces as described in Japanese patent application provisional publication Nos. 58-33424 (1983), and 58-205723 (1983). According to this type, ultrasonic vibrations are dispersed into both vertical and lateral directions with respect to the fuse-bonding surface, so that the oblique type provides those advantages over vertical and lateral vibration type sealing apparatus. That is, in the oblique vibration type sealing apparatus, foreign materials adhered to the fuse-bonding surfaces of the sheets can be removed in a lateral direction of the sheets, and simultaneously lateral displacement of the sheets relative to the horn and anvil can be prevented to some extent. Therefore, fuse-bonding is achievable at higher-efficiency in the oblique type as compared to the vertical or lateral vibration type. Accordingly, the oblique vibration type sealing apparatus is also available for fuse-bonding at least two multiple layer sheets together, such bonding being insufficient in lateral vibration type apparatus.
However, lateral displacement of the sheets still cannot be completely eliminated in the latter type, and the displacement occurs despite formation of the embossed pattern as shown in FIGS. 12A and 12B at the contact surfaces of the horn and anvil. Therefore, further improvement on fuse-bonding has been required by way of highly efficient transmission of the ultrasonic vibration to the surfaces to be fuse-bonded.
Transmission efficiency of the ultrasonic vibration in the lateral or oblique vibration type sealing apparatus is determinative by the shape of projection pattern to be embossed at the horn and anvil surfaces which support the sheets. In this case, attention should be drawn to the following aspects:
(a) The horn and/or anvil should provide maximum area in contact with the fuse-bonding surfaces in a direction parallel therewith so as to generate maximum frictional heat at the fuse-bonding surfaces; and
(b) The embossed pattern should provide sufficient thrust or bite with respect to the fuse-bonding surfaces so as to eliminate displacement of the latter relative to the horn and anvil.
Regarding aspect (a), maximum contact area in a direction parallel with the fuse-bonding surfaces is obtainable, if the embossed pattern is not formed on the horn and anvil. However, in the case lateral displacement of the sheets is excessively promoted. On the other hand, regarding aspect (b), the tip end of the projection pattern should be formed at an acute angle. However, in this case there is no contact area in a direction parallel with the fuse-bonding surfaces, to thereby degrade transmission of the ultrasonic vibration to the fuse-bonding surfaces, so that frictional heat is hardly generated. Apparently, these are contradictory requirements between the aspects (a) and (b).
As a matter of example, referring to the conventional embossed pattern shown in FIGS. 12A and 12B, projections 5 each having a rectangular flat contact face are defined by the formation of obliquely oriented diagonal grooves 4 intersecting with one another. The projections 5 have upright surfaces 41 directed perpendicular to the contact surface of the structure, each of the projections 5 does not easily bite into the fuse-bonding surfaces, so that lateral displacement of the sheets is not completely avoidable.
Further, U.S. Pat. No. 3,468,731 appears to show an embossed pattern having a construction similar to that shown in FIGS. 12A and 12B. In FIG. 4 of the U.S. patent, a knurled area is provided at a sealing surface. However, the knurling serves to increase the localized sealing pressure and simultaneously provides a most pleasing appearance of the sealed area (see column 3 lines 71 to 74 of the above-mentioned U.S. patent). Such structure also does not surely prevent the sheets from lateral displacement, as in the case shown in FIGS. 12A and 12B.
Furthermore, Japanese utility model application provisional publication 60-201928 (1985) shows a horn 1 in which a plurality of grooves and ridges 42 extend in a longitudinal direction of the contact surface as shown in FIGS. 13A to 13C herein. The grooves have constant depth along their length, and the ridges have contact height along their length with their tops being chamfered. As shown in FIG. 13C, the cross-sectional shape at the contact surface 3 of the horn is that of a continuous sinusoidal curve in the lateral direction of the contact surface 3. However, this publication pertains to a vertical vibration type ultrasonic sealing apparatus as is apparent from FIG. 13A in which the ultrasonic vibration direction is along the axial direction of the horn 1, and the contact surface 3 is formed at the distal end of the horn. For this it is understood that vibration is applied to the fuse-bonding surfaces of the sheets in a direction perpendicular thereto. Accordingly, these ridges 42 are not formed for the purpose of preventing the lateral displacement of the sheets, but are formed for the purpose of guiding resin melted by the frictional heat attendant ultrasonic vibration into the grooved area at the sealing portion, to thereby hold the molten resin in that area, to thus enhance fuse-bonding performance. Even if such structure shown in FIGS. 13A through 13C is applied to the lateral or oblique vibration type sealing apparatus, sufficient frictional heat may not be generated, since no contact surfaces directed parallel to the fuse-bonding surfaces are acknowledgeable in the ridge zone 42 having sinusoidal cross-section, and such ridge zone 42 may not sufficiently prevent the lateral displacement of the sheets due to insufficient biting of the ridge zone 42 into the fuse-bonding surfaces.
Conventional ultrasonic sealing apparatus still provides drawbacks from another vantage point. In case of sealing the bottom portion of a tubular member by the employment of the conventional apparatus, a clamp means 20 (so called "Jaw") is required as shown in FIGS. 14-16 for clamping a container 17 prior to clamping the bottom portion of the container 17 by a horn and an anvil. The clamp means 20 includes a frame member 21 in which a slide member 22 is slidably disposed. The slide member 22 is urged by a spring 23 so as to clamp a bottom of a container 17 by the frame member 21 and the slide member 22 with the aid of biasing force of the spring 23. A pair of guide plates 24 extend obliquely and downwardly from the bottom portions of the frame 21 and the slide member 22, so that cylindrical tubular container 17 is introduced into a space defined between the frame 21 and the slider 22 to be flattened by the guide plates 24.
The above-described clamp means 20 is required so as to hold the members to be fuse-bonded, since complete fuse-bonding may not be carried out in the conventional sealing apparatus. Such clamp means 20 therefore serves as a supplement to complete fuse-bonding. Further the clamp means 20 also prevents molten resin generated at fuse-bonding surfaces during ultrasonic vibration from entering inside the tubular container 17, since the clamp means 20 clamps the bottom portion of the container at the position below the fuse-bonding surfaces (see FIG. 14).
On the contrary, the disposal of the clamp means 20 leads to other disadvantage.
Firstly, molten resin is accumulated between a space defined between a portion clamped by the clamp means 20 and a portion clamped by the horn 1 and anvil 2 (see FIG. 14). Therefore, a bulged portion 25 is disadvantageously provided at this space as shown in FIGS. 17A and 17B, to thereby degrade external appearance.
Secondly, such clamp means complicates the production line. To be more specific, the conventional sealing apparatus as shown in FIG. 14 includes the clamp means 20, a feed-in conveyor 31 adapted to transfer non-fuse-bonded tubular container 17, a turntable 32 adapted to mount a plurality of the clamp means 20 at its outer peripheral end portion, a horn 1 and anvil 2 those positioned at one side of the turntable 32, and a feed-out conveyor 33 adapted to take-up a tubular container subjected to fuse-bonding by the horn 1 and the anvil 2. Container holders 34 are respectively provided on these feed-in and feed-out conveyors 31 and 33 so as to supply the container 17 to the clamp means 20 or receive the container therefrom. Each of the holders 34 also provides includes a liftable mechanism for that purpose.
If the clamp means 20 is eliminated, the container holder 34 having liftable mechanism and the turn-table 32 can also be eliminated, and further, a single conveyor can perform both feed-in and feed-out functions. As a result, a compact and simplified production line may be provided if the clamp means 20 can be eliminated.